1. Field of the Invention
The present invention relates to a method of manufacturing a wiring substrate, a liquid ejection head and an image forming apparatus, and more particularly, to technology for manufacturing a wiring substrate having a conductive through hole and a non-conductive through hole.
2. Description of the Related Art
Inkjet recording apparatuses are known which comprise a head (liquid ejection head) having a plurality of nozzles, and which record images onto a recording medium by ejecting ink toward the recording medium from the head.
In a head of this type, ink droplets are ejected from nozzles by selectively driving ejection elements (for example, piezoelectric elements or heat generating elements) corresponding to the nozzles. For this purpose, the head is provided with a wiring substrate comprising wires for supplying drive signals to the ejection elements. In a wiring substrate of this kind, conductive through holes for creating electrical connections and non-conductive through holes for supplying ink are required.
As a method for forming such conductive layers selectively, for example, Japanese Patent Application Publication No. 7-231158 discloses a method in which a plating activation treatment film or protection film is transpired by a pattern radiation based on a laser light, thereby selectively forming plating layers. Japanese Patent Application Publication No. 8-230195 discloses a method of selectively forming plating layers by two shot injection molding of a plastic material which can be plated and a plastic material which cannot be plated.
Since, in order to improve the quality of the recorded image, the number of nozzles should be increased, then there arises a need to arrange an extremely large number of conductive and non-conductive through holes at high density in the wiring substrate. However, a method of manufacture has not yet been proposed which makes it possible to obtain a highly reliable wiring substrate having conductive and non-conductive through holes at low costs. For example, there is a method in which conductive paste is filled into or plating is carried out while parts to be non-conductive on a substrate having holes are masked; however, it is difficult to achieve good masking accuracy and positioning accuracy, and therefore it is difficult to obtain good reliability for a substrate.
Moreover, although the technologies disclosed in Japanese Patent Application Publications No. 7-231158 and No. 8-230195 have been proposed as methods for forming conductive parts and non-conductive parts on a wiring substrate, there are problems of the following kinds when these technologies are applied to conductive parts and non-conductive parts of through holes. According to the technology in Japanese Patent Application Publication No. 7-231158, although the pattern radiation by laser light is used, it is difficult to radiate laser light uniformly inside the through holes. Furthermore, the technology in Japanese Patent Application Publication No. 8-230195 can be used in the case of a low-density arrangement of holes, but, in the case where a large number of through holes are to be arranged at high density, it is difficult to make a die and to carry out molding. In both case, there is a problem in that it is difficult to form conductive layers selectively in a large number of through holes arranged at high density.